Aerosol–cloud interactions remain a major uncertainty in estimating human influence on climate. Here, we diagnose how aerosols, clouds, radiation, and ocean coupling interact in the Taiwan Earth System Model version 1 (TaiESM1). We use two complementary diagnostic methods to separate cloud radiative responses, aerosol-mediated effects, and the roles of aerosol–cloud and aerosol–radiation interactions. The contrast between the historical simulation and the pre-industrial control simulation produces a strongly negative total cloud radiative response (−2.08 W m⁻²), dominated by an aerosol-mediated component (−2.24 W m⁻²), despite a positive global-mean cloud feedback (+0.84 W m⁻² K⁻¹). This cooling is concentrated over the North Pacific and North Atlantic, where changes in low- and middle-level clouds are associated with stronger reflection of solar radiation. The shortwave aerosol effective radiative forcing is −2.34 W m⁻², mainly from aerosol–cloud interactions (−2.00 W m⁻²), while aerosol–radiation interactions are weaker (−0.34 W m⁻²). Within the aerosol–cloud component, cloud scattering dominates (−2.14 W m⁻²), whereas cloud-amount changes are small and positive (+0.12 W m⁻²). Compared with selected Coupled Model Intercomparison Project Phase 6 models, TaiESM1 lies near the strong aerosol–cloud cooling end of the sample. Fully coupled and prescribed-sea-surface-temperature simulations indicate that ocean coupling mainly alters regional patterns rather than the global-mean magnitude. These results identify cloud scattering of sunlight as the dominant driver of TaiESM1’s aerosol-related cloud cooling and highlight aerosol activation, cloud droplet number, and cloud optical depth as priorities for model development.